Behavior of wake vortices near the ground over a large range of Reynolds numbers

Numerical simulations based on the two-dimensional vorticity-stream functio n formulation are used to investigate the behavior of wake vortices near th e ground over a wide Reynolds number range and to determine the maximum hei ght the primary vortices reach far downstream of the lifting wing. All case s within the studied Reynolds number range (3.10(2) less than or equal to R e-r less than or equal to 3.10(6)) show the separation of boundary layer vo rticity from the ground, the formation of vortices in the separation region and one or several rebounds of the primary vortex pair. The amount of circ ulation produced within the boundary layer shows only minor variations, whi le an increasing Reynolds number results in an increasing number of generat ed vortices with decreasing circulation. The minimum altitude of the primar y vortex pair increases with a decreasing Reynolds number, while the maximu m altitude far downstream does not show a regular dependence on the Reynold s number. For all Reynolds numbers the maximum altitude of the primary vort ices far downstream is smaller than 3.1 times their initial spacing. This r esult is confirmed by theoretical deductions yielding an upper limit for th e maximum altitude of the primary vortices after several rebounds. (C) Else vier, Paris.